Universal joint cross of power transmissions and a method of its heat treatment

ABSTRACT

A universal joint cross for power transmissions, said cross including a base having arms adapted to be engaged by bearing needles, said cross being made of a steel consisting essentially of 0.4 to 1.2 percent carbon and 0.1 to 0.3 percent manganese, the surface hardness of the arms at their points of contact with said bearing needles being in the range of 60 to 67 Rockwell C, and at the points near the base being in the range of 50 to 56 Rockwell C. The method of heat treatment comprises the steps of heating said cross to its hardening temperature, cooling said cross to obtain a hardened surface layer and then nonuniformly tempering said cross.

United States Patent Ostrovsky et al.

[54] UNIVERSAL JOINT CROSS OF POWER TRANSMISSIONS AND A METHOD OF ITSHEAT TREATMENT Oct. 31, 1969 Appl. No.: 872,889

[22] Filed:

[30] Foreign Application Priority Data Oct. 31, 1968 U.S.S.R ..l279470[151 3,655,466 [451 Apr. 11,1972

[52] U.S.Cl ..148/145,148/36, 148/39, 148/146, 148/150, 148/152, 148/154[51] Int. Cl. ..C21d H18 [58] Field ofSearch ..148/l43, 145, 146, 150,152, 148/154, 36, 39

[5 6] References Cited UNITED STATES PATENTS 3,466,202 9/1969 Hrusovsky..l48/152 Primary Examiner-Richard 0. Dean Attorney-Waters, Roditi,Schwartz & Nissen [5 7] ABSTRACT A universal joint cross for powertransmissions, said cross including a base having arms adapted to beengaged by bearing needles, said cross being made of a steel consistingessentially of 0.4 to 1.2 percent carbon and 0.1 to 0.3 percentmanganese, the surface hardness of the arms at their points of contactwith said bearing needles being in the range of 60 to 67 Rockwell C, andat the points nearthe base being in the range of 50 to 56 Rockwell C.The method of heat treatment comprises the steps of heating said crossto its hardening temperature, cooling said cross to obtain a hardenedsurface layer and then nonuniformly tempering said cross.

5 Claims, 4 Drawing Figures UNIVERSAL JOINT CROSS OF POWER TRANSMISSIONSAND A METHOD OF ITS HEAT TREATMENT The present invention relates to theuniversal joint crosses of power transmissions and to the methods oftheir heat treatment.

In the course of operation, the arms of the universal joint cross arebent to a certain extent and the bearing sleeves with needles turn inrelation to the surface of said arms. This causes heavy static, impactand contact loads. To withstand these loads, the crosses have beenmanufactured up to the present time from case-hardened alloy steels.Practical experience in using the universal joint crosses has shown thathigh resistance to contact loads can be attained by case-hardening 1.82.2 mm deep which calls for a long holding time (over 20 hours) and alow-temperature tempering. However, the increased depth of thecarburized layer increases brittleness of the cross and reduces itsresistance to the static and impact loads.

The known cross is of a uniform hardness throughout its surface; thisfails to ensure an optimum combination of surface hardness with strengthof the cross since the different sections of the latter are subjected todifferent loads. The cylindrical surfaces of the cross arms in the zoneof the bearing needles are subjected to heavy contact loads. Hence,these sections of the cross must be especially hard. On the other hand,the sections near the base of the cross arm must have a higherresistance to static and impact bending. Therefore, the hardness ofthese sections must be lower in order to reduce brittleness.

The known cross is made of expensive alloy steels; its heat treatment,including case hardening, hardening and low-temperature tempering takesmuch time; still this process fails to ensure the optimum strength ofthe cross.

An object of the present invention is to eliminate the aforesaiddisadvantages.

The main object of the present invention resides in providing auniversal joint cross with a higher structural strength and a longerservice life along with a lower cost by changing the grade of steel andintroducing a special method of its heat treatment.

An object of the present invention resides in providing a universaljoint cross with a higher structural strength and a longer service lifeand featuring a higher resistance to static and impact loads.

Another object of the invention is to provide a cheaper universal jointcross made from cheap steel, and to simplify the process of its heattreatment.

Other objects and advantages of the present invention will becomeapparent from the description that follows and the accompanyingdrawings.

The abovementioncd and other objects are achieved by providing auniversal joint whose different sections are subjected to differentloads which, according to the invention, is made of a low-hardeningsteel containing 0.4 to 1.2% carbon and 0.1 to 0.3% manganese and whichhas arms whose surface hardness at the point of contact with the bearingneedles varies from 60 to 67 Rock.C. while near the base of the arms itranges from 50 to 56 Rock.C.

It is preferable that the metal of the cross should contain 0.6% carbon,0.17% manganese, 0.13%C chromium, 0.2% nickel and 0.04% titanium.

For manufacturing said cross we hereby claim a method of its heattreatment wherein the cross is hardened and then tempered. According tothe invention, the cross arms in the zones of contact with the bearingneedles are heated to l-200 C within 6 12 seconds while in the sectionsnear the arm bases to a temperature of 450 to 650 C also in the courseof 6 to 12 seconds.

It is practicable that tempering should be carried out by heating theentire cross simultaneously.

The present invention is based on the characteristics of the steelproposed for making the crosses and on the principle of conformity ofthe properties of the material in every area of the article with thenature and the value of the leads acting thereon.

The steel, having the content of components according to the presentinvention, for example, 0.6% carbon, 0. l7% manganese; 0.13% chrome;0.2% nickel; 0.04% titanium, has a high decomposition rate of austenitein the 500-700 C. temperature range, where the formation of perlitestructure takes place. Such a steel has a lower hardenability thancommon carbon steels.

This, in effect, means that a cross made from such a steel acquires amartensite structure upon intensive cooling after through heating forhardening, having a hardness of more than 60 Rockwell C only in thesurface layer, but not throughout its cross-section. In deep layers ofthe cross made from the proposed steel, the transformation of austenitetakes place in accordance with the perlite mechanism, which results information of a troostite-sorbite mixture having a hardness of 35-40Rockwell C.

The cross made from the proposed steel has the same distribution ofhardness throughout the section of the cross arms as if it were made ofa case-hardened alloy steel, i.e., a shell having a high degree ofhardness in its surface layer, and a strong and viscous core in its deeplayers. Such a hardness distribution through the cross-section of thearms of the cross insures the provision of compressive residual stressesin the surface layer. This prevents a cracking when the cross is beinghardened, and concurrently increases the resistance of the cross tocyclic (fluctuating) and contact forces.

The non-uniform distribution of hardness in the surface layer of thecross, along the length of the arm, as proposed in the presentinvention, may be explained by the following reasons:

In proximity to the base of the arm working stresses act which areconditioned by the action of the bending moments. In order to increasethe resistance of the cross in response to the working tensile stressesit is necessary to increase the viscosity of the steel in these areas,or essentially to increase the resistance to embrittlement fractures.The simplest way to do this is to reduce the hardness of themartensite-hardened steel to 50-56 Rockwell C. The hardness reduction atthe base of the arms only leads to an increase in resistance to staticand bending loads of the entire cross. In the areas of the arms wherebearing needles are supported, the value of tensile stresses isconsiderably lower than at the base of the arm. In this regiondestruction of the steel is caused by high contact stresses, theresistance to which is correlated with the hardness on the basis of thehigher the hardness, the greater the contact durability of the steel.Therefore, the cross arms are provided with a hardness of 60-65 RockwellC, at the points of contact with the bearing needles, and with theproperties of the steel in every area or region of the cross arm beingadapted to correspond with the character of the leads acting thereon.

Thus, realization of the present invention improves radically thestructural strength and extends the service life of the universal jointcross, reduces considerably its cost owing to the use of the cheapcarbon steel instead of the expensive alloy steel, decreases the amountof work required for heat treatment and allows a possibility ofautomating the process of cross manufacture directly in the productionline.

Now the invention will described by way of example with reference to theaccompanying drawings in which:

FIG. 1 is a schematic view of the universal joint cross complete with aneedle bearing;

FIG. 2 is a diagram of induction heating of the universal joint crossfor nonuniform tempering according to the claimed method;

FIG. 3 is the macrostructure of the universal joint cross made oflow-hardening steel heat-treated according to the claimed method;

FIG. 4 is the macrostructure of the universal joint cross made of alloysteel and heat-treated according to the known method.

The universal joint cross is a solid body 1 (FIG. 1) with fourprotruding arms 2. Mounted on each arm is a bearing 3 with a sleeve 4and needles 5. Glands 6 and 7 are intended to keep the lubricant insidethe bearing. The bearings 3 are provided on all the four arms 2 of thecross.

High contact stresses are originated during the operation on the sectionof the arm 2 contacting the bearing needles 5. The sections of the arm 2free of the bearing needles (those located under the sealing glands 6and 7) are not subjected to high contact stresses. The static and impactloads create maximum stresses at the base of the arms 2 along sectionI-l, that is at the points where high resistance to contact loads is notrequired. The sections of the arm 2 with a high resistance to thecontact loads may have a lower resistance to the tensile stressesoriginated by the bending forces; conversely, the sections effectivelywithstanding the tensile stresses may possess a low resistance tocontact loads. Therefore, if we retain a high hardness 60 Rock.C.) ofthe arms 2 at the points of contact with the bearing needles 5 andreduce it to 50-56 Rock.C. near the arm where maximum tensile stressesoccur, we can combine a high resistance to contact loads with a higherhardness of the entire article. A reduction of hardness to 50-56 Rock.C.near the arm base is quite allowable because at these points the armscontact the sealing glands 6 and 7 and are not subjected to heavycontact loads.

These requirements are satisfied by the claimed universal joint crossillustrated in FIG. 1. This cross is made of a lowhardening steelcontaining 0.4 to 1.2% carbon, preferably section contacting the bearingneedles remains above 60 Rock.C. while at its base it drops to 50-56Rock.C.

For the sake of comparison, FIG. 4 shows the macrostructure of theuniversal joint cross made of an alloy steel and heat treated by a knownmethod. In this macrostructure the carburized layer of martensite 12with a hardness exceeding 60 Rock.C. occupies the entire surface of thecross; the deeper layers are constituted by low-carbon martensite 13with a hardness of 35-40 Rock.C.

It can be seen from the above that the surface hardness of the arm 2 atthe points of contact with the bearing needles 5 and that of the core ofthe claimed cross are equal to the hardness of the correspondingsections of a case-hardened cross.

However, the claimed cross is considerably cheaper, it is made ofanon-alloy steel, it does not require prolonged case hardening and itssurface layer near the arm base has a lower hardness which raises thestrength of the entire article.

The tests have shown that the claimed universal joint cross,

com ared with the cross made of alloy steel with a casehar ened layer1.6-2.0 mm deep has a resistance to static bending 75-80 percent higher,while the resistance to impact failure is 300 percent higher, theresistance to brinel1ing being equal. This can be seen from the appendedTable.

TABLE [Strength characteristics of universal joint cross obtained bystatic and impact bending tests] Max-imum bending moment Impact understatic strength 'Iime, Steel Method of heat treatment load, kgm. kgm.hours Low-hardening steel, Hardening after deep induction heating,non-uniform eIectric tempering ensuring 1, 250 75 90 distribution ofhardness along cross arm to suit operational requirements from 63 toMn=0.17%, 50 Rock. 0. with a hardened layer 2 mm deep and deeper.Cr=0.13%, Ni=0.2%, Ti=0.04%. C =0 2%, Cr=1 0%, Case hardening 1.6-2 mm.deep, hardening, uniform electric tempering in oil quenching 700 90 1=.0%, bath at 180 0. within 90 minutes to 61 Rock. 0. Ti=0.05%, P 0.003%.

1 Before brinelling appears during closedcircuit stand tests with 220kgm. torque on cross.

0.6%, and from 0.1 to 0.3 manganese, preferably 0.17%. Besides, themetal of the cross contains 0.13% chromium, 0.2% nickel and 0.04%titanium. The hardness of the cross arms 2 at the points of contact withthe bearing needles 5 is within 60 and 67 Rock.C. while on the sectionsnear the arm base it is from 50 to 56 Rock.C.

The method of heat treatment of the universal joint cross made from theabove-mentioned low-hardening steel and possessing nonuniform hardnessalong the arm 2 consists in hardening followed by induction heating fortempering, in which the temperature near the arm base reaches 450-650 Cwhile at the points of the arm contact with the bearing needles 5 itranges from 100 to 200 C, the heating time being 6 to 12 seconds.

For the implementation of this method, the inductor conductors 8 (FIG.2) provided with magnetic circuits 9 are placed near the cross as shownin FIG. 2. With such an an rangement of the inductor, the currentdensity is higher near the base of the arms 2, being lower at their faceends. In view of a short heating time (6 to 12 seconds) the equalizingeffect of heat conduction is virtually nonexistent so that the sectionsof the arm contacting the bearing needles 5 and located near the faceends, are tempered at comparatively low temperatures l00-200 C) whiletheir sections located near the cross centre are tempered atconsiderably higher temperatures (450 to 650 C).

When the cross made of a low-hardening steel is being hardened, itsentire surface becomes covered with a layer of martensite 10 (FIG. 3)with a hardness of 65-67 Rock.C. more than 1.5 mm deep, while under thislayer there is a layer of troostite with a hardness of -40 Rock.C. Afterthis nonuniform induction tempering the hardness of the arm 2 on theWhat we claim is:

l. A universal joint cross for power transmissions whose varioussections support different loads in operation, said cross including abase having arms adapted to be engaged by bearing needles; said crossbeing made of a steel consisting essentially of 0.4 to 1.2% carbon and0.1 to 0.3% manganese, the surface hardness of the arms at their pointsof contact with said bearing needles being in the range of from to 67Rockwell C, and at the points near the base being in the range of from50 to 56 Rockwell C.

2. A universal joint cross according to claim 1 comprising essentially0.6% carbon and 0.17% manganese.

3. A universal joint cross according to claim 1 comprising essentially0.13% chromium, 0.2% nickel, and 0.04% titani- 4. A method of heattreatment of a universal joint cross for power transmissions havingdifferent sections adapted to carry different loads in operation, saidcross inciuding a base having arms adapted to be engaged by bearingneedles, and said cross being made of a steel consisting essentially of0.4 to 12% carbon and 0.1 to 0.3% manganese, said method comprising thesteps of: heating said cross to its hardening temperature, intensivelycooling said cross to obtain a hardened surface layer, heating saidcross for tempering to a range in which the cross arms at their pointsof contact with the bearing needles are heated to a temperature of to200 C. for a period of 6 to 12 seconds, and at their points adjacent thebase to 450 to 650 C. for a period of 6 to 12 seconds.

5. A method according to claim 4 comprising simultaneously heating theentire cross for tempering.

2. A universal joint cross according to claim 1 comprising essentially0.6% carbon and 0.17% manganese.
 3. A universal joint cross according toclaim 1 comprising essentially 0.13% chromium, 0.2% niCkel, and 0.04%titanium.
 4. A method of heat treatment of a universal joint cross forpower transmissions having different sections adapted to carry differentloads in operation, said cross including a base having arms adapted tobe engaged by bearing needles, and said cross being made of a steelconsisting essentially of 0.4 to 1.2% carbon and 0.1 to 0.3% manganese,said method comprising the steps of: heating said cross to its hardeningtemperature, intensively cooling said cross to obtain a hardened surfacelayer, heating said cross for tempering to a range in which the crossarms at their points of contact with the bearing needles are heated to atemperature of 100* to 200* C. for a period of 6 to 12 seconds, and attheir points adjacent the base to 450* to 650* C. for a period of 6 to12 seconds.
 5. A method according to claim 4 comprising simultaneouslyheating the entire cross for tempering.